Orthopedic implant having a porous metal pad

ABSTRACT

The invention is directed to a method of making an orthopaedic implant. An orthopaedic implant body is formed which has a supporting surface. A porous metal pad is formed to fit the supporting surface of the body. The porous metal pad is clamped and/or adhesively bonded to the supporting surface. A laser beam is coupled between the porous metal pad and the implant body at a plurality of locations so as to form a coalescence of metal between the porous metal pad and the body.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. patent application Ser. No.08/609,210 now U.S. Pat. No. 5,672,284, filed Mar. 1, 1996, entitled"ORTHOPAEDIC IMPLANT AND METHOD OF MAKING SAME", which is a continuationof U.S. patent application Ser. No. 08/228,774, filed Apr. 18, 1994,entitled "ORTHOPAEDIC IMPLANT AND METHOD OF MAKING SAME", now U.S. Pat.No. 5,504,300, which is a divisional of 08/652,193 filed May 23, 1996U.S. Pat. No. 5,773,789.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to orthopaedic implants, and, moreparticularly, to orthopaedic implants having a porous metal pad attachedthereto.

2. Description of the Related Art

Orthopaedic implants, such as knee or hip implants, may include one ormore porous surfaces at the exterior thereof. The porous surfacesenhance implant fixation within the bone by allowing bony ingrowththerein or penetration of bone cement. The porous surface is typicallyin the form of a pad constructed of fiber metal, metal beads or a wiremesh. The fibers, beads or wires are typically interconnected with eachother using a sintering or diffusion bonding process. The porous metalpad is cut to shape to fit a supporting surface formed on theorthopaedic implant body.

One known method of attaching the porous metal pad to the implant bodyis to clamp the porous metal pad against the supporting surface of theimplant body, and thereafter metallurgically bond the porous metal padto the implant body using a diffusion bonding or sintering process. Aproblem with sintering the porous metal pad to the implant body is thatthis process is both time consuming and expensive from a manufacturingstandpoint. For example, during sintering, the ramp up and cool downtime for a sintering furnace is approximately 14 hours per cycle. If theporous metal pad is being connected, e.g., to the interior bone engagingsurface of a femoral knee component, it may take a minimum of threecycles to complete the sintering operation. The complex geometricinterior design of the femoral knee component may require that only oneor two porous metal pads be attached to the femoral knee componentduring one cycle of the sintering process. The typical interior of thefemoral knee component defines five distinct surfaces which requireconnection with a porous metal pad. Therefore, to completely bond theporous metal pad to the interior of the femoral knee component mayrequire in excess of 42 hours of furnace time. Added to this is the timerequired to connect the clamping tool to the implant for holding theporous metal pad in contact with the supporting surface of the implant.It is thus apparent that providing a porous metal pad on an implantusing a sintering process is relatively time consuming and expensive.

It is also known to diffusion bond a fiber metal pad to a thin metalfoil, which in turn is attached to an orthopaedic implant body using alaser welding process. For details of such an attachment process,reference is hereby made to U.S. patent application Ser. No. 08/609,210,entitled "ORTHOPAEDIC IMPLANT AND METHOD OF MAKING SAME," which isassigned to the assignee of the present invention and incorporatedherein by reference. In general, a porous metal pad, such as a fibermetal pad, is diffusion bonded to a thin metal foil. The fiber metal padand thin metal foil are each configured to be received within a recessformed in the orthopaedic implant body. The edges of the thin metal foilextend to the exterior of the recess formed in the orthopaedic implantbody. A laser welder is used to weld the thin metal foil to theorthopaedic implant body, and thereby indirectly attach the fiber metalpad to the implant body.

What is needed in the art is a method of attaching a porous metal pad toan orthopaedic implant body wherein the porous metal pad is attached tothe implant body at locations other than the periphery of the porousmetal pad.

What is further needed in the art is a method of attaching a porousmetal pad to an implant body which is faster than a sintering process.

SUMMARY OF THE INVENTION

The present invention provides a method of attaching a porous metal padto a body of an orthopaedic implant by coupling a laser beam between theporous metal pad and the body at a plurality of predetermined locations.

The invention comprises, in one form thereof, a method of making anorthopaedic implant. An orthopaedic implant body is formed which has asupporting surface. A porous metal pad is formed to fit the supportingsurface of the body. The porous metal pad is clamped and/or adhesivelybonded to the supporting surface. A laser beam is coupled between theporous metal pad and the body at a plurality of locations, so as to forma coalescence of metal between the porous metal pad and the body.

An advantage of the present invention is that the porous metal pad isattached to the orthopaedic implant body without using the relativelyslow process of diffusion bonding or sintering.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a perspective view of an embodiment of a femoral kneecomponent manufactured using the method of the present invention;

FIG. 2 is an enlarged, fragmentary view showing interconnection betweena porous metal pad and a body of an orthopaedic implant using the methodof the present invention;

FIGS. 3-5 illustrate different embodiments of patterns at which theporous metal pad is laser welded to the implant body; and

FIG. 6 is a flowchart illustrating an embodiment of the method of thepresent invention.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate one preferred embodiment of the invention, in one form, andsuch exemplifications are not to be construed as limiting the scope ofthe invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIGS. 1 and 2,there is shown an embodiment of an orthopaedic implant manufacturedusing the method of the present invention. In the embodiment shown, theorthopaedic implant is in the form of a femoral knee component 10,including an orthopaedic implant body 12 and a porous metal pad 14.

Body 12 includes a plurality of adjoining, generally planar supportingsurfaces for supporting and attachment with porous metal pad 14, one ofwhich is shown and referenced 16 in FIG. 2. Body 12 is formed from amaterial such as cobalt-chromium alloy, titanium alloy or stainlesssteel alloy.

Porous metal pad 14 is placed against supporting surface 16 of body 12,and attached thereto in a manner as will be described hereinafter.Porous metal pad 14, in the embodiment shown, is in the form of a fibermetal pad 14 having a plurality of metal fibers 18 which areinterconnected together in a known manner, such as by using a sinteringor diffusion bonding process. Fiber metal pad 14 is preferably formedfrom a material such as cobalt-chromium alloy, titanium alloy orstainless steel alloy.

Fiber metal pad 14 is attached to body 12 by coupling a laser beam (notshown) between fiber metal pad 14 and body 12, so as to form acoalescence of metal between fiber metal pad 14 and body 12. The processof "coupling" using a laser means that enough energy is transferred intothe material to melt the material. An example of a laser which may beutilized with the present invention is a YAG industrial lasermanufactured by Lumonics Corporation, Livonia, Mich., USA, although manyother types of commercially available lasers can also be used with themethod of the present invention. More particularly, the laser beam iscoupled between fiber metal pad 14 and body 12 at a plurality oflocations indicated generally by reference numbers 20. As the laser iscoupled between fiber metal pad 14 and body 12, a portion of fibermetals 18 and body 12 melt to define a weld bead which interconnectsfiber metal pad 14 and body 12 upon cooling. The weld bead may be in theform of a substantially cylindrical layer 22 which extends through fibermetal pad 14 and into body 12. Cylindrical layer 22 has a diameter whichcorresponds to a diameter of the laser beam. In the embodiment shown inthe drawings, cylindrical layer 22 has an outside diameter "D" ofbetween approximately 0.020 and 0.050 inch and preferably approximately0.30 inch.

Although the weld bead produced by the coalescing of material betweenfiber metal pad 14 and body 12 is shown as a substantially cylindricallayer 22 in FIG. 2, it is also to be understood that the weld bead maybe in the form of a cone, solid bead or other shape. The shape of theweld bead is primarily dependent upon the density of metal fibers 18which the laser beam contacts.

The laser utilized with the present invention is adjusted so that thepower and beam diameter correspond to the particular type of porousmetal pad 14 which is used. For example, a cobalt-chromium-molybdenumfiber metal pad 14 may be placed in a light box in such a way as toallow light passing through the pores of the fiber metal pad 14 to bedetected by a video camera. Digitized images of the pores in the fibermetal pad may be captured with a computer assisted image analysissystem. The size distribution of the through pores in the fiber metalpad may be used to estimate a minimum laser beam diameter which isrequired for the production of quality weldments. The laser beamdiameter may be adjusted, e.g., by changing the angle of the reflectivemirror in the laser. A laser beam diameter of between approximately0.015 and 0.030 inch has been found effective to produce a weld diameterof between approximately 0.020 and 0.050 inch.

The phrase "laser beam welding", or other derivative spellings thereof,as used in this application, is intended to mean welding using a highenergy source, such as laser beam welding, electron beam welding, plasmawelding, etc.

Referring now to FIG. 6, there is shown a flow chart illustrating anembodiment of the method of the present invention. First, a porous pador fiber metal pad 14 is formed or fabricated in known manner using asintering or diffusion bonding process (block 24). The fiber metal padis then laser cut into a shape which mates with supporting surface 16 ofbody 12 (block 26). The fiber metal pad may be formed as a continuouspiece which extends from one supporting surface to another. The fibermetal pad may also be coined if desired (block 26). Thereafter, fibermetal pad 14 is attached to supporting surface 16 of body 12 using anadhesive (block 28). Alternatively, fiber metal pad 14 may be clampedagainst supporting surfaces 16, as indicated schematically by arrows 30in FIG. 1. After fiber metal pad 14 is adhesively bonded or clamped tobody 12, a laser beam is coupled between fiber metal pad 14 and body 12at a plurality of locations 20 (block 32). The mixture of melted andsubsequently cooled metal of fiber metal pad 14 and body 12 welds fibermetal pad 14 to body 12. The orthopaedic implant is then annealed orsolution heat treated (block 34), and the previously applied adhesiveremoved.

As indicated above, the laser beam is coupled between fiber metal pad 14and body 12 at a plurality of locations. The plurality of weldmentlocations 20 may correspond to a predetermined pattern or a randompattern. Laser weldment locations 20 preferably have a spacingtherebetween of approximately 0.040 and 0.150 inch, and more preferablya spacing of approximately 0.070 inch. Referring to FIGS. 3-5, threedifferent possible patterns of laser weldment locations are shown. FIG.3 illustrates a plurality of weldment locations which define asubstantially square pattern. Each laser weld location 20 has a diameterD (FIG. 2) of between 0.10 and 0.60 inch, and preferably approximately0.40 inch. Dimensions between adjacent laser weld locations 20,indicated by reference number 36, are approximately 0.80 inch; and thedimension from corner to corner, indicated by reference number 38, isapproximately 0.113 inch.

FIG. 4 illustrates a plurality of weldment locations 20 defining asubstantially square pattern with a centrally positioned weldinglocation 20 therein. Each weldment location 20 preferably has a diameterD of approximately 0.40 inch. Dimensions 40 are approximately 0.031inch; dimensions 42 are approximately 0.100 inch; dimension 44 isapproximately 0.060 inch; and dimension 46 is approximately 0.141 inch.

FIG. 5 illustrates a plurality of weldment locations 20 which define asubstantially hexagonal pattern, including a centrally located weldmentlocation 20.

In the embodiment shown, orthopaedic implant 10 is in the form of afemoral knee component. However, it is also to be understood that themethod of the present invention may be used with other orthopaedicimplants, such as a hip, shoulder, elbow or ankle implant, or apermanently implanted fixation rod.

Moreover, in the embodiment shown, porous metal pad 14 is in the form ofa fiber metal pad. However, it is also to be understood that other typesof porous metal pads such as a beaded pad or wire mesh may also beutilized with the method of the present invention.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

What is claimed is:
 1. An orthopaedic implant comprising, a metal bodyhaving at least one supporting surface, a porous metal pad contactingthe supporting surface, the porous metal pad being connected to theimplant body by a coalescence of metal between said porous metal pad andthe body formed by a plurality of weld beads, wherein a portion of saidweld beads are generally tubular having a diameter between 0.10 inchesand 0.60 inches and is spaced between 0.040 inches and 0.150 inchesapart from one another.
 2. The implant of claim 1 wherein the diameterof the weld beads is about 0.40 inches.
 3. The implant of claim 1wherein the weld beads are about 0.070 inches apart from one another.